FIG. 3.

Signature sequence for MFS transporters compared with the corresponding sequence of the human FLVCR. The MFS signature sequence, which occurs in the hydrophilic loop that separates TM2 and TM3, is the most highly conserved sequence in this transporter superfamily. The sequence for FLVCR is shown at the top, and residues identical to the consensus are boxed. Other MFS transporter sequences are also shown for C. elegans (accession no. AF002196) and for the bacterial glucarate transporter (GlucarateT) (accession no. P42237) and glycerol-3-phosphate transporter (G3PT) (accession no. AJ235270). In addition, the consensus sequences are shown for the ACS, OPA, and monocarboxylate porter (MCP) subfamilies of the MFS transporters (38). The bottom line shows the overall consensus sequence for all MFS transporters as compiled by Pao et al. (38). In this line, each amino acid is indicated by a subscript, which indicates its frequency of occurrence in the consensus sequences of the 17 distinct lineages of MFS transporters. For example, glycine (G) at position 1 occurs in 11 of the 17 subfamilies whereas G at position 8 occurs in 15 of the 17 subfamilies. The similarity score for each sequence is the sum of these subscript score for each corresponding position. Random sequences would have very low average similarity scores.